1. Field of the Invention
The present invention relates to a computer graphics rendering apparatus and a computer graphics rendering method.
2. Background Art
In the field of computer graphics, a method called texture mapping is widely known. In the texture mapping, it is possible to give texture to an object in an image, by pasting a texture image on the surface of the object. In the texture mapping, in order to realize an increase in speed of image processing, plural texture images having different resolutions are often used to represent the texture. Each of the texture images is called mipmap. The level of the resolution of each texture image is represented by a number called a mipmap level.
In such texture mapping, plural texture images having different mipmap levels may be simultaneously referred to. In this case, accesses to these images occur simultaneously in a texture cache. Therefore, a conflict of a cache line may occur among these images. In other words, a same cache line may be used for these images.
In general, such conflict can be prevented by adopting a set associative approach of two or more ways (hereinafter referred to as “associative approach”) or an approach of dividing a cache into two sets such as a set for mipmaps at even levels and a set for mipmaps at odd levels (hereinafter referred to as “division approach”) (see, for example, Ziyad S. Hakura and Anoop Gupta, Stanford University, “The Design and Analysis of a Cache Architecture for Texture Mapping”, International Symposium on Computer Architecture, 1997). However, in the associative approach, an increase in a circuit cost due to an increase in associativity poses a problem. Further, in the division approach, it is likely that only a half of the total capacity of the cache is used in some case. Therefore, in the division approach, deterioration in efficiency of the cache poses a problem. For example, when texture is given to a large object, only a mipmap at level 0 is used even if a mipmap function is adopted. In this case, a half of the total capacity of the cache (a set for odd levels) is not used at all.
As described above, in the associative approach and division approach, wastes related to caching of texture images, such as an increase in a circuit cost and deterioration in efficiency of the cache, pose problems.